System and method for heat storage and release with flange

ABSTRACT

The invention also relates to a system and a method for energy storage and recovery using the system and the method for heat storage and recovery.

FIELD OF THE INVENTION

The present invention relates to the field of energy storage bycompressed gas, notably air (CAES—Compressed Air Energy Storage). Inparticular, the present invention relates to an AACAES (AdvancedAdiabatic Compressed Air Energy Storage) system wherein storage of thegas and storage of the heat generated is provided.

BACKGROUND OF THE INVENTION

In a compressed-air energy storage (CAES) system, the energy that isdesired to be used at a later time is stored as compressed air. Forstorage, the energy, in particular electrical energy, drives aircompressors, and for de-storage, the compressed air drives turbines thatmay be connected to an electric generator. The efficiency of thissolution is not optimal because part of the energy of the compressed aircomes in form of heat that is not used. Indeed, in CAES methods, onlythe mechanical energy of the air is used, i.e. all of the heat producedupon compression is discharged. By way of example, compressed air at 8MPa (80 bar) heats up during compression to about 150° C., but it iscooled prior to storage. Furthermore, the system requires heating thestored air to achieve expansion of the air. Indeed, if the air is storedat 8 MPa (80 bar) and at ambient temperature, and if it is desired torecover the energy by expansion, decompression of the air again followsan isentropic curve, but this time from the initial storage conditions(about 8 MPa and 300 K). The air thus cools down to temperatures thatare not realistic (83 K, i.e. −191° C.). It is therefore necessary toheat it, which can be done using a gas burner, or another fuel.

Several variants currently exist for this system. The following systemsand methods can notably be mentioned:

-   -   ACAES (Adiabatic Compressed Air Energy Storage), where the air        is stored at high temperature due to compression. However, this        type of system requires a specific storage system, bulky and        expensive (adiabatic storage),    -   AACAES (Advanced Adiabatic Compressed Air Energy Storage), where        the air is stored at ambient temperature, and the heat due to        compression is also stored, separately, in a heat storage system        TES (Thermal Energy Storage). The heat stored in the TES system        is used to heat the air prior to expansion.

A first solution considered for the heat storage system TES consists inusing a heat transfer fluid allowing to store the heat resulting fromcompression in order to release it into the atmosphere prior toexpansion by means of heat exchangers. For example, patent applicationEP-2,447,501 describes an AACAES system where oil used as the heattransfer fluid circulates in a closed loop to exchange heat with air.Besides, patent applications EP-2,530,283 and WO-2011/053,411 describean AACAES system where heat exchanges are carried out by a heat transferfluid circulating in a closed loop, the closed loop comprising a singleheat transfer fluid tank.

However, the systems described in these patent applications requirespecific means for storage and circulation of the heat transfer fluid.Furthermore, for these systems, significant pressure drops are generatedby the heat exchangers used.

A second solution considered for the heat storage system TES is based ona static heat storage (without displacement of the bed of heat storageparticles or of the heat transfer fluid). In this case, the heat storagemeans can be made up of one or more fixed bed(s) of heat storageparticles. Upon charging, the hot compressed gas flows through the heatstorage means. Through heat exchange between this gas and the storageparticles, the latter are heated and the compressed gas is cooled.Likewise, when discharging, the heat exchange generated between thestorage particles and the compressed gas cools the storage particles andheats the compressed gas. The fixed bed of storage particles isgenerally held in the storage means by a holding structure, which maydirectly be the wall of the storage means, or a structure mounted insidethe storage means. When charging or discharging the heat storage system,the temperature of the fixed bed in a plane orthogonal to the compressedgas flow is substantially homogeneous, except in the vicinity of theholding structure. Indeed, the proximity of the wall induces, in thegranular structure of the medium, a particular arrangement of theparticles with respect to the wall (edge effect). This particulararrangement has an incidence on the velocity profile of the gas flows atthe wall and, therefore, on the temperature profile of the particles.

As a result, the thermal gradient along a section orthogonal to thecompressed gas flow is zero, or nearly zero, except at the holdingstructure juxtaposed with the fixed bed, on the periphery of the fixedbed: this shows that the temperature is homogeneous or nearlyhomogeneous in this section orthogonal to the axis of the compressed gasflow, except on the periphery of the fixed bed, at the holdingstructure. This temperature profile heterogeneity in the fixed bedinduces a loss of the overall efficiency of the storage means and a lossof the overall performance of the system.

In order to overcome these drawbacks, and in particular to limit theefficiency loss related to the edge effect, the present inventionrelates to a heat storage means consisting of at least one fixed bed ofheat storage particles. Inside the storage means, at least one obstacle,orthogonal or substantially orthogonal to the air flow, is positioned onthe periphery of the bed of storage particles. This obstacle is arrangedalong the periphery of the fixed bed (continuously or discontinuously).It allows the compressed gas flow to be removed locally from the end ofthe fixed particle bed and, therefore, from the holding structurejuxtaposed with the fixed bed, thus reducing the edge effect by theholding structure.

SUMMARY OF THE INVENTION

The invention relates to a heat storage and release system comprising atleast one storage enclosure, at least one fixed bed of heat storage andrelease particles being arranged in said storage enclosure, and at leastone fluid can flow through said fixed bed in said storage enclosure,said storage enclosure comprising at least one inlet of said fluid intosaid storage enclosure and at least one outlet of said fluid from saidstorage enclosure, characterized in that at least one obstacle ispositioned in said fixed bed, substantially perpendicular to thecirculating flow of said fluid, said obstacle being positioned on theperiphery of said fixed bed of said heat storage and release particles,said obstacle being distributed around the periphery of said fixed bedof said storage particles.

According to a variant of the invention, the system comprises at leasttwo obstacles evenly spaced along said circulating flow of said fluid.

Preferably, the spacing between two successive obstacles along saidcirculating flow of said fluid is at minimum twice the dimension of saidobstacle, perpendicular to said circulating flow of said fluid.

According to an embodiment of the invention, said storage enclosurecomprises at least one distributor for distributing said fluid into saidfixed bed, and preferably at least two distributors.

Preferably, said obstacle is positioned at said distributor.

According to one implementation, said obstacle consists of a plate.

Advantageously, the dimension of said obstacle, perpendicular to saidcirculating flow of said fluid, ranges between 1 and 10 times theequivalent Sauter diameter of said heat storage and release particles ofsaid fixed bed, preferably between 3 and 5 times the equivalent Sauterdiameter of said heat storage and release particles of said fixed bed.

According to an embodiment, said storage enclosure is cylindrical orsubstantially cylindrical.

According to a variant embodiment, said circulating flow of said fluidwithin said storage enclosure occurs along the axis of said storageenclosure.

Advantageously, said obstacle consists of an annular plate arranged onthe inner face of the cylindrical wall of said storage enclosure.

According to another variant embodiment, said circulating flow of saidfluid within said storage enclosure occurs along an axis perpendicularto the axis of said storage enclosure, at least two trays supportingsaid fixed bed being positioned within said storage enclosure, saidsupport trays being perpendicular to the axis of said storage enclosure.

Advantageously, said obstacle is positioned on said support trays, saidobstacle thus forming a portion of a cylinder on each of the two trayssupporting said fixed bed of said heat storage and release particles.

According to an embodiment, said obstacle is continuously distributedaround the periphery of said fixed bed.

Alternatively, said obstacle is discontinuously distributed around theperiphery of said fixed bed.

The invention also relates to a compressed-gas energy storage andrecovery system, comprising at least one gas compression means, at leastone compressed gas storage means, at least one means of expanding saidcompressed gas to generate energy and at least one heat storage meansaccording to one of the above features.

The invention also relates to a heat storage and recovery method whereinthe following steps are carried out:

a) storing the heat in a fixed bed of heat storage and releaseparticles, by circulating a fluid in said fixed bed, and

b) releasing the heat recovered by said fixed bed, by circulating afluid in said fixed bed.

To store and release the heat, said fluid is subjected to at least oneobstacle positioned in the fixed bed, perpendicular or substantiallyperpendicular to the flow of said fluid, said obstacle being positionedon the periphery of said fixed bed of said heat storage and releaseparticles, said obstacle being distributed around the periphery of saidfixed bed of said heat storage and release particles.

According to a variant of the invention, said fluid flows through astepped arrangement made up of a plurality of said fixed beds containedin said heat storage and release means.

According to an embodiment, said heat storage and release means has asubstantially cylindrical shape.

According to a variant, said fluid flows radially through said fixed bedof said heat storage and release means.

Alternatively, said fluid flows axially through said fixed bed of saidheat storage and release means.

The invention also relates to a compressed-gas energy storage andrecovery method, wherein the following steps are carried out:

a) compressing a gas,

b) cooling said compressed gas by heat exchange with a fixed bed of heatstorage and release particles,

c) storing said cooled gas,

d) heating said cooled compressed gas by releasing the heat of saidfixed bed of said heat storage and release particles, and

e) expanding said heated compressed gas so as to generate energy, andwherein heat storage and release is carried out according to the heatstorage and release method according to one of the above features.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the system and of the method accordingto the invention will be clear from reading the description hereafter ofembodiments given by way of non-limitative example, with reference tothe accompanying figures wherein:

FIG. 1 illustrates a heat storage and release system according to oneembodiment of the invention,

FIG. 2 illustrates a heat storage and release system according to asecond embodiment of the invention,

FIG. 3 illustrates a heat storage and release system according to athird embodiment of the invention,

FIG. 4 illustrates a heat storage and release system according to afourth embodiment of the invention,

FIG. 5 illustrates the temperature distribution in a plane perpendicularto the direction of circulation of the fluid according to a heat storageand release system of the prior art,

FIG. 6 shows a comparison of the evolution of temperatures over time fortwo diametrically opposite points of two heat storage and releasesystems, a first one according to the prior art and a second accordingto the invention, and

FIG. 7 illustrates a compressed-gas energy storage and recovery systemaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a heat storage and release system. Inthis implementation, a fluid (compressed gas for example) flows througha fixed bed of heat storage and release particles enabling thermalexchange between the fluid and the particles. The particles are selectedfrom a material capable of storing and releasing heat.

The system according to the invention comprises:

-   -   at least one storage enclosure,    -   at least one fluid flowing through the storage enclosure,    -   at least one fixed bed of heat storage and release particles.        These solid particles, hereafter referred to as “storage        particles”, exchange heat with the fluid during the heat storage        and release phases, the heat being stored in the particles        between these two phases. According to the invention, the heat        storage particles are distributed over at least one fixed bed. A        fixed bed is understood to be an arrangement of heat storage        particles where the particles are stationary. The heat storage        particles allow the gas to pass through the fixed bed,    -   at least two fluid inlets/outlets at the storage enclosure, the        direction of flow being reversed between the heat storage and        release operations. Preferably, the inlets/outlets can be        located at ends remote from the fixed bed,    -   at least one obstacle positioned in the fixed bed, perpendicular        or substantially perpendicular to the circulating flow of the        fluid, on the periphery of the fixed bed of storage particles,        the obstacle being distributed around the periphery of the fixed        bed, in a continuous or discontinuous manner,        -   by obstacle positioned perpendicular or substantially            perpendicular to the circulating flow of the fluid, it is            understood that the principal plane of the obstacle (for            example the plane of the plate in case of an annular plate)            is orthogonal or substantially orthogonal to the circulating            flow of the fluid,        -   the obstacle is positioned on the periphery of the fixed bed            of storage particles: when the fixed bed is delimited by            walls, for example the walls of the storage enclosure or of            the plates supporting the fixed bed, the obstacle may be            positioned in contact with the wall of the storage enclosure            or with the support plates, positioned on the periphery of            the fixed bed,        -   by obstacle distributed around the periphery of the fixed            bed, it is understood that the profile of the obstacle is            distributed over the major part of the fixed bed periphery,            preferably substantially the entire periphery of the fixed            bed. For example, for a cylindrical enclosure, it may be            represented by an annular plate (continuously distributed            obstacle) or by an annular plate with holes (continuously            distributed obstacle), possibly evenly distributed over the            plate, or by a multiplicity of small plates evenly            distributed (discontinuously distributed obstacle) over the            entire inner cylinder of the enclosure. The presence of this            obstacle allows to locally remove the fluid from the fixed            bed periphery, thus improving the temperature homogeneity            within the fixed bed of particles, and therefore the overall            efficiency of the unit. Indeed, a more homogeneous            temperature profile in a plane perpendicular to the            circulating flow of the fluid provides better thermal            exchanges between the fluid and the fixed bed of storage            particles. The overall performances of the storage system            are therefore improved. Besides, the nature of the obstacle            generates no significant pressure drop increase, therefore            it does not impact the overall operation of the heat storage            and release system.

Each fixed bed can comprise solid particles or particles containing aphase change material (PCM). The particles may thus come in form ofcapsules containing PCMs. Using PCM-containing particle beds allows tobetter control the thermal gradient in the tank by applying differentmelting temperatures. A compromise between efficiency and cost can alsobe found by mixing PCMs and sensible heat storage materials in the samebed. The following materials can be used for the PCMs: paraffins, whosemelting temperature is below 130° C., salts melting at temperaturesabove 300° C., (eutectic) mixtures allowing to have a wide meltingtemperature range.

The solid particles (whether phase change particles or not) can have allthe known forms of conventional granular media (balls, cylinders,extrudates, trilobes, etc.) and any other form allowing to maximize thesurface of exchange with the gas. The particle size can range between0.5 mm and 10 cm, preferably between 2 mm and 50 mm, and more preferablybetween 5 mm and 20 mm.

The temperature range within which the heat storage means can operate isbetween 0° C. and 500° C., preferably between 100° C. and 400° C., andmore preferably between 100° C. and 350° C. The temperature levelsdepend both on the complete AACAES process and on the type of materialused for the particles of the heat storage means.

According to an implementation of the invention, the system can compriseat least two obstacles evenly spaced along the circulating flow of thefluid. The presence of these evenly spaced obstacles improves thetemperature homogeneity and therefore the performance. For example, theobstacles can be positioned at the inlets/outlets of the fixed bedand/or in the middle and, preferably, at the inlet, in the middle and atthe outlet of the fixed bed. This configuration provides an optimizeddistribution of the heat flow in the fixed bed.

According to a variant embodiment of the invention, the spacing betweenthe two successive obstacles can be at minimum equal to twice thedimension of the obstacle perpendicular to the circulating flow. Indeed,by observing this minimum spacing, the flow that is locally diverted bythe obstacle towards the center of the fixed particle bed can again comeclose to the walls of the bed prior to encountering the next obstacle.Thus, the gas flow coming near to the next obstacle is very close towhat it would be if the previous obstacle did not exist.

According to a variant embodiment of the invention, the storageenclosure can comprise at least one distributor. A distributor isunderstood to be a device allowing the fluid to be distributed ashomogeneously as possible in the fixed bed of storage particles, so asto optimize thermal exchanges between the fluid and the fixed bed ofstorage particles. Preferably, at least two distributors can beprovided, the first one at one end of the fixed bed of storage particlesand the second at the other end of the fixed bed of storage particles.For example, when the fluid circulates in a given direction of flow(upon charging for example), the first distributor can be arranged atthe inlet of the fixed bed of storage particles, just before the fluidenters the fixed bed of storage particles, and the second distributorcan be arranged at the outlet of the fixed bed of storage particles,just after the fluid flows from the fixed bed of storage particles. Whenthe fluid circulates upon discharging, in the opposite direction offlow, the second distributor is then located at the gas entry in thefixed bed of storage particles, just before the fluid enters the fixedbed of storage particles, and the first distributor is then at the gasexit from the fixed bed of storage particles, just after the outlet ofthe fixed bed of storage particles. Alternatively, other distributorsmay be added and positioned within the fixed bed of storage particles.

According to an embodiment of the invention, the obstacle can bepositioned at the distributor. Thus, the local acceleration and thedisplacement of the gas flow by synergy between the presence of theobstacle and the presence of the distributor are improved.

According to an embodiment of the invention, the obstacle can consist ofa plate. This design enables simple and inexpensive manufacturing of theobstacle. Besides, the plate needs not be mechanically fixed, whichsimplifies the implementation thereof and makes the invention usablewhen modernizing or revamping a unit. In this case, the plate lies onthe fixed bed of particles.

According to a feature of the invention, the dimension of the obstacleperpendicular to the circulating flow of the fluid can be equal to avalue between 1 and 10 times the equivalent Sauter diameter of thestorage particles, preferably between 3 and 5 times the equivalentSauter diameter of the storage particles. What is referred to as theequivalent Sauter diameter is the characteristic value of the storageparticles d₃₂ defined by:

${d_{32} = {6 \cdot \frac{V_{p}}{A_{p}}}},$

with V_(p) the particle volume and A_(p) the particle surface area. Thisfeature of the invention allows to limit the pressure drop induced bythe obstacle while optimizing the effect of the presence of the obstacleon the temperature evolution in a plane perpendicular to the circulatingflow of the fluid.

According to an embodiment of the invention, the storage enclosure maybe cylindrical or substantially cylindrical.

Furthermore, the circulating flow of the fluid within the cylindrical orsubstantially cylindrical storage enclosure may occur along the axis ofthe storage enclosure. One speaks then of “axial flow” to designate thisfluid circulation mode within the storage enclosure and of “axial flowsystem” to designate a heat storage and release system with an axialflow circulation mode of the fluid.

Moreover, the obstacle in the cylindrical or substantially cylindricalstorage enclosure can be an annular plate. This type of obstacle is easyto manufacture, inexpensive, and it meets the requirement of localremoval of the circulating fluid flow from the fixed bed periphery.

Alternatively, the circulating flow of the fluid within the cylindricalor substantially cylindrical storage enclosure may occur along an axisperpendicular to the storage enclosure axis. In this case, one speaks of“radial flow” for the fluid circulation within the storage enclosure andof “radial flow system” to designate a heat storage and release systemwith a radial flow circulation mode of the fluid. Trays referred to as“support trays” can therefore be used and positioned within the storageenclosure. Their purpose is to hold the fixed beds of storage particlesand to orient the circulating flow of the fluid in the radial directionwithin the storage enclosure.

In the radial flow system, the obstacle can be positioned on the supporttrays. The obstacle is then divided into two parts, a first partpositioned on the so-called “upper” support tray and a second part onthe so-called “lower” support tray. On each of these two support trays,the obstacle represents for example a portion of a cylinder.

According to an embodiment, the obstacle can be continuously distributedaround the periphery of the fixed bed, for example, by a plate or aflange (a collar). This allows to use an easily manufactured form.

Alternatively, the obstacle can be discontinuously distributed aroundthe periphery of the fixed bed, for example by means of severalobstacles distributed over the circumference. This affords the advantageof having several elements of smaller size, more easily transportable,which can be more readily set and positioned in the storage means.

FIGS. 1 to 3 show non-limitative examples of embodiments of anaxial-flow heat storage and release system according to the invention.

FIG. 1 schematically shows, by way of non-limitative example, a heatstorage and release means 10 equipped with a storage enclosure 1, afixed bed 2 of storage particles and a fluid whose circulation 3 ismaterialized by arrows. In storage mode, the fluid circulation occursthrough an inlet 8 in storage enclosure 1 to an outlet 9 of storageenclosure 1. In release mode, fluid circulation 3 can be reversed instorage enclosure 1: the fluid then flows in through inlet 9 and outthrough outlet 8. Storage enclosure 1 comprises two distributors 5 andan obstacle 4 positioned on the periphery of fixed bed 2, obstacle 4being perpendicular to circulating flow 3 of the fluid, obstacle 4 beingalso distributed and continuous over the periphery of fixed bed 2 andpositioned on the periphery of fixed bed 2. In the example of FIG. 1,obstacle 4 is an annular plate. Alternatively, other forms of obstaclesmay be used.

FIG. 2 schematically shows, by way of non-limitative example, a variantembodiment where two obstacles 4 are arranged in storage enclosure 1, onthe periphery of fixed bed 2, perpendicular to circulating flow 3. Thesetwo obstacles are continuous around the periphery of fixed bed 2. Thecharacteristic dimension of obstacle 4 perpendicular to circulating flow3 of the fluid is materialized by the letter L. For example, for anobstacle 4 that would come in form of an annular plate as in FIG. 2, Lcorresponds to the width of the annular plate. The spacing between twosuccessive obstacles 4 is materialized by distance E, in the directionof circulating flow 3. Preferably, dimension L can be equal to a valuebetween 1 and 10 times the equivalent Sauter diameter of the storageparticles, more preferably between 3 and 5 times the equivalent Sauterdiameter of the storage particles. Preferably also, spacing E can be atminimum equal to twice dimension L of the obstacle perpendicular to thecirculating flow.

FIG. 3 schematically shows, by way of non-limitative example, an exampleof a variant embodiment of the invention where several obstacles areused, notably an obstacle 4 is positioned at the inlet and outletdistributors 5. Alternatively, obstacle 4 can also be positioned at oneor the other of inlet or outlet distributors 5, or on an intermediatedistributor that would be positioned inside fixed bed 2 (not shown).FIG. 3 also shows an obstacle positioned at a level where there is nodistributor.

FIG. 4 schematically shows, by way of non-limitative example, aradial-flow heat storage and release system 20. In this example, thesystem comprises 6 layers of fixed beds 2, each layer having an annularsection. In storage mode, the fluid flows through inlet 8 into thestorage enclosure. In heat release mode, the fluid flow can be reversed.Then, the circulating flow materialized by the arrows is directed bysupport trays 6 which alternately send the flow from the centre of theenclosure to the outside or from the outside of the enclosure to thecentre, depending on the number and the position of fixed bed 2. Thepart on the right-hand side of FIG. 4 shows for example two differentways of positioning obstacles 4 in this radial flow system 20. Thediagram at the top right shows two obstacles 4 positioned atdistributors 5 at the inlet and the outlet of each fixed bed 2. Thediagram at the bottom right shows an obstacle 4 positioned approximatelyat mid-width of fixed bed 2, i.e. equidistant from the two distributors5 at the inlet and the outlet of each fixed bed 2. It is noted that, forthe two diagrams of the right-hand part, obstacle 4 is divided into twoparts, each part being a cylindrical wall of axis merging with the axisof the storage enclosure, an upper part positioned at the top of fixedbed 2, close to the so-called upper support tray 6, and a lower part atthe bottom of fixed bed 2, close to the so-called lower support tray 6.These examples are not limitative: other obstacle numbers, otherobstacle positions and other obstacle forms may be considered.

FIG. 5 shows the temperature iso-contours at a time t during heatstorage in a fixed bed of storage particles for a heat storage andrelease system according to the prior art, i.e. without obstacles. Theshades of grey in FIG. 5 indicate temperature variations. The evolutionof temperature front 25 in a plane orthogonal to circulating flow 3 ofthe fluid illustrates that:

-   -   the temperature front is nearly constant in a plane orthogonal        to circulating flow 3, seen from the vicinity of the centre of        the fixed bed,    -   local temperature evolutions 7 are obtained near the periphery        of the fixed bed.

These local temperature evolutions reflect a non-homogeneity oftemperature profile 25 in a plane orthogonal to the direction of flow ofthe fluid. This lack of homogeneity induces a drop in performance of theheat storage and release system. The present invention allows to limitor even to avoid these local temperature evolutions in the fixed bed.

The present invention also relates to a compressed-gas energy storageand recovery system, comprising:

-   -   at least one gas compression means,    -   at least one compressed gas storage means,    -   at least one compressed gas expansion means,    -   at least one heat storage and release means according to at        least one variant described above. The heat storage and release        means is positioned between the compression or expansion means        and the compressed gas storage means.

By using the heat storage and release means according to the invention,the thermal performances of the compressed-gas energy storage andrecovery system are optimized and, therefore, the overall efficiency ofthe compressed-gas energy storage and recovery system is increased.

Preferably, several compression and expansion stages can be used inorder to optimize the overall performances of the system. In this case,at least one heat storage and release means can be arranged between twocompression or expansion stages. The number of stages and the ratio ofeach stage can be selected according notably to the gas and to thevarious constraints of the system to improve the cost/quality ratio.

The gas used may notably be air, for example air taken from the ambientmedium.

Preferably also, several compressed gas storage tanks can be used. Eachof these tanks may have different characteristics, for example differentvolumes and/or pressures.

Preferably, several heat storage and release means can also be used, andeach of which may have different characteristics so as to optimize theoverall operation of the system.

The compression means can notably be a compressor and the expansionmeans can notably be a turbine.

FIG. 7 schematically illustrates, by way of non-limitative example, anembodiment of an AACAES system according to the invention. In thisfigure, the arrows in solid line illustrate the circulation of the gasduring the compression steps (energy storage), and the arrows in dottedline illustrate the circulation of the gas during the expansion steps(energy release). This figure illustrates an AACAES system with a singlecompression stage 40, a single expansion stage 50 and a heat storagesystem 10. The system comprises a compressed gas storage tank 30. Heatstorage system 10 is interposed between compression/expansion stage 40or 50 and compressed gas storage tank 30. The heat storage system isproduced according to at least one variant embodiment described above.Conventionally, in the energy storage phase (compression), the air isfirst compressed in compressor 40, then cooled in heat storage system10. The cooled compressed gas is stored in tank 30. The heat storageparticles of heat storage system 10 are hot due to the cooling of thecompressed gas in the compression phase. Upon energy recovery(expansion), the stored compressed gas is heated in heat storage system10. Then, the gas conventionally flows through one or more expansionstages 50 (one stage in the example illustrated in FIG. 7).

The present invention also relates to a heat storage and release methodwherein the following steps are carried out:

a) storing the heat in a fixed bed of heat storage and releaseparticles, by circulating a fluid in the fixed bed, and

b) releasing the heat recovered by the fixed bed, by circulating a fluidin the fixed bed,

and wherein, to store and release the heat, the fluid is subjected to atleast one obstacle positioned in the fixed bed, perpendicular orsubstantially perpendicular to the circulating flow of the fluid, theobstacle being positioned on the periphery of the fixed bed of storageparticles, the obstacle being distributed around the periphery of thefixed bed of storage particles, continuously or discontinuously. Thepresence of the obstacle thus positioned in the heat storage and releasemeans allows to locally remove the circulating flow of the fluid fromthe fixed bed periphery. This generates a local change in the velocityfield and therefore in temperature, which allows the temperature in theparticle bed to be homogenized. Thus, the thermal performances of themethod are improved.

The fluid used for heat release may be identical to or different fromthe fluid used for heat storage.

According to a variant embodiment of the method according to theinvention, the fluid can flow through a stepped arrangement made up of aplurality of fixed beds contained in the heat storage and release means.The system can thus be optimized regarding various criteria such as, byway of non-limitative example, efficiency improvement or manufacturingcost minimization.

According to an embodiment of the method according to the invention, thefluid can circulate through a cylindrical or substantially cylindricalheat storage and release means. This particular geometric shape has theadvantage of being easy to manufacture and it allows the circulatingflow of the fluid to be readily and homogeneously directed through theheat storage and release means.

According to a variant embodiment of the method according to theinvention, the fluid can flow radially through the fixed bed of the heatstorage and release means, i.e. in a direction perpendicular to the axisof the cylindrical or substantially cylindrical heat storage and releasemeans. The specific feature of the radial flow allows to betterhomogenize the temperatures inside the storage enclosure in relation toan axial flow and, therefore, to improve the thermal performances of theheat storage and release means.

Alternatively, the fluid can flow axially through the fixed bed of theheat storage and release means, i.e. the direction of flow of the fluidis colinear with the axis of the heat storage and release means. Byusing an axial-flow heat storage and release method, the method iseasier to implement and the overall cost of the process can beminimized.

Furthermore, the present invention also relates to a compressed-gasenergy storage and recovery method, wherein the following steps arecarried out:

a) compressing a gas,

b) cooling said compressed gas by heat exchange with a fixed bed ofstorage particles,

c) storing the cooled gas,

d) heating the cooled compressed gas by release of the heat from thefixed bed of storage particles, and

e) expanding the heated compressed gas so as to generate energy,

wherein heat storage (compressed gas cooling) and release (compressedgas expansion) is carried out according to the heat storage and releasemethod described above. Using the heat storage and release methodaccording to at least one of the variants described above in the energystorage and recovery method allows the heat storage and releaseperformances to be improved. Improving these performances allows theoverall compressed-gas energy storage and recovery performances to beimproved.

The gas used may notably be air, for example air taken from the ambientmedium.

Steps b) and d) may be preferably implemented by the heat storage andrelease system according to at least one variant described above.

The compression and/or expansion steps can be broken down into severalcompression and/or expansion sub-steps. This can improve the overallperformances of the system and/or optimize the overall cost/qualityratio according to the constraints of the system and the gas used. It isalso possible to use standard compression and/or expansion means, whichallows to limit the design and manufacturing costs of specificcompression and/or expansion elements if necessary.

The compression and expansion steps can notably be carried out by acompressor and a turbine respectively. During expansion, the turbine cangenerate electrical energy. If the gas is air, the expanded air can bedischarged into the ambient medium.

Step c) can be carried out within a compressed gas storage means whichmay be a natural reservoir or not (an underground cavity for example).The compressed gas storage means can be above or below ground.Furthermore, it can consist of a single volume or of a plurality ofvolumes, interconnected or not. During storage, the compressed gasstorage means is closed.

The method and the system according to the invention can be used forstoring intermittent energy, such as wind or solar power, so as to beable to use this energy at the desired time.

Comparative Example

FIG. 6 shows a comparative example of implementation of the invention.This figure illustrates the temperature evolution at two diametricallyopposite points A and B, positioned at mid-height of the heat storageenclosure, for two different axial-flow cylindrical heat storage andrelease means. The first heat storage and release system corresponds toa system according to the prior art (without obstacle) and the secondsystem corresponds to an embodiment according to the invention (with theconfiguration of FIG. 1). Curves A1 and B1 give the temperatureevolutions over time at points A and B for the heat storage and releasesystem according to the prior art; curves A2 and B2 give the temperatureevolutions over time at points A and B for a heat storage and releasesystem according to an embodiment of the invention. Three zonesidentified by the letters E, S and R, respectively corresponding todurations during which the system accumulates heat (zone E), stores theheat thus accumulated (zone S), then releases the stored heat (zone R),are notably distinguished on these curves. The two heat storage andrelease systems are identical, except for the addition of the obstacleto the system according to an embodiment of the invention. It can beseen in FIG. 6 that the temperature peaks observed on curves A1 and B1are significantly reduced on curves A2 and B2. Besides, the averagetemperature over the storage duration is higher, which shows betterperformance of the system according to the invention in relation to thesystem according to the prior art.

1. A heat storage and release system comprising at least one storageenclosure, at least one fixed bed of heat storage and release particlesbeing arranged in the storage enclosure, and at least one fluid can flowthrough the fixed bed in the storage enclosure, the storage enclosurecomprising at least one inlet of the fluid into the storage enclosureand at least one outlet of the fluid from the storage enclosure, whereinat least one obstacle is positioned in the fixed bed, substantiallyperpendicular to the circulating flow of the fluid, the obstacle beingpositioned on the periphery of the fixed bed of the heat storage andrelease particles, the obstacle being distributed around the peripheryof the fixed bed of the storage particles.
 2. A system as claimed inclaim 1, wherein the system comprises at least two obstacles evenlyspaced along the circulating flow of the fluid.
 3. A system as claimedin claim 2, wherein the spacing (E) between two of the successiveobstacles along the circulating flow of the fluid is at minimum twicethe dimension of the obstacle, perpendicular to the circulating flow ofthe fluid.
 4. A system as claimed in claim 1, wherein storage enclosurecomprises at least one distributor for distributing the fluid into thefixed bed, and preferably at least two distributors.
 5. A system asclaimed in claim 4, wherein the obstacle is positioned at thedistributor.
 6. A system as claimed in claim 1, wherein the obstacleconsists of a plate.
 7. A system as claimed in claim 1, whereindimension (L) of the obstacle, perpendicular to the circulating flow ofthe fluid, ranges between 1 and 10 times the equivalent Sauter diameterof the heat storage and release particles of the fixed bed, preferablybetween 3 and 5 times the equivalent Sauter diameter of the heat storageand release particles of the fixed bed.
 8. A system as claimed in claim1, wherein the storage enclosure is cylindrical or substantiallycylindrical.
 9. A system as claimed in claim 8, wherein the circulatingflow of the fluid within the storage enclosure occurs along the axis ofthe storage enclosure.
 10. A system as claimed in claim 9, wherein theobstacle consists of an annular plate arranged on the inner face of thecylindrical wall of the storage enclosure.
 11. A system as claimed inclaim 8, wherein the circulating flow of the fluid within the storageenclosure occurs along an axis perpendicular to the axis of the storageenclosure, at least two trays supporting the fixed bed being positionedwithin the storage enclosure, the support trays being perpendicular tothe axis of the storage enclosure.
 12. A system as claimed in claim 11,wherein the obstacle is positioned on the support trays, the obstaclethus forming a portion of a cylinder on each of the two trays supportingthe fixed bed of the heat storage and release particles.
 13. A system asclaimed in claim 1, wherein the obstacle is continuously distributedaround the periphery of the fixed bed.
 14. A system as claimed in claim1, wherein the obstacle is discontinuously distributed around theperiphery of the fixed bed.
 15. A compressed-gas energy storage andrecovery system, comprising at least one gas compression means, at leastone compressed gas storage means, at least one means of expanding thecompressed gas to generate energy and at least one heat storage means asclaimed in claim
 1. 16. A heat storage and recovery method, wherein thefollowing steps are carried out: a) storing the heat in a fixed bed ofheat storage and release particles, by circulating a fluid in the fixedbed, and b) releasing the heat recovered by the fixed bed, bycirculating a fluid in the fixed bed, wherein, to store and release theheat, the fluid is subjected to at least one obstacle positioned infixed bed, perpendicular or substantially perpendicular to flow of thefluid, the obstacle being positioned on the periphery of the fixed bedof the heat storage and release particles, the obstacle beingdistributed around the periphery of the fixed bed of the heat storageand release particles.
 17. A method as claimed in claim 16, wherein thefluid flows through a stepped arrangement made up of a plurality of thefixed beds contained in the heat storage and release means.
 18. A methodas claimed in claim 16, wherein the heat storage and release means has asubstantially cylindrical shape.
 19. A method as claimed in claim 18,wherein the fluid flows radially through the fixed bed of the heatstorage and release means.
 20. A method as claimed in claim 18, whereinthe fluid flows axially through the fixed bed of the heat storage andrelease means.
 21. A compressed-gas energy storage and recovery method,wherein the following steps are carried out: a) compressing a gas, b)cooling the compressed gas by heat exchange with a fixed bed of heatstorage and release particles, c) storing the cooled gas, d) heating thecooled compressed gas by releasing the heat of the fixed bed of the heatstorage and release particles, and e) expanding the heated compressedgas so as to generate energy, and wherein heat storage and release iscarried out according to the heat storage and release method as claimedin claim 16.